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Roost Environments for Bats 

Using Abandoned Mines 

in Southwestern Montana: 

A Preliminary Assessment 



Prepared for: 



U.S. Bureau of Land Management 
Dillon Field Office 

Agreement Number 1422E930A960015 

Prepared by: 
Paul Hendricks and David Kampwerth 



March 2001 




MONTANA 



Natural Heritage 
Program 



Roost Environments for Bats 

Using Abandoned Mines 

in Southwestern Montana: 

A Preliminary Assessment 



© 2001 Montana Natural Heritage Program 

State Library Building • P.O. Box 201 800 • 1 5 1 5 East Sixth Avenue • Helena, MT 59620-1 800 • 406-444-3009 



This document should be cited as follows: 

Hendricks, P., and D. Kampwerth. 200 1 . Roost environments for bats using abandoned mines 
in southwestern Montana: a preliminary assessment. Report to the U.S. Bureau of Land 
Management. Montana Natural Heritage Program, Helena. 19 pp. 



Executive Summary 



Roost environments often abandoned mine 
workings known to be used by bats were studied 
in detail during 1 998-1 999 to expand on scant 
knowledge of underground roost requirements for 
bats in Montana. Objectives were to: ^docu- 
ment daily mine ambient temperature and relative 
humidity during winter and summer using elec- 
tronic dataloggers, especially at underground 
microsites where evidence of bat use was found, 
2) document the seasons when mines were used 
for roosting, and identify the bat species using the 
mines, and 3) determine mine characteristics 
obtained from external surveys that might be useful 
for identifying underground environments suitable 
for bat roosts in abandoned mines. Special 
attention was paid to Townsend's Big-eared Bat 
(Corynorhinus townsendii), a Montana animal 
species of special concern, a Montana BLM 
Special Status species, and a species of high 
conservation concern throughout its range. 

Four bat species were identified using these mines. 
Townsend's Big-eared Bat (Corynorhinus 
townsendii) was present at six mines, Western 
Small-footed Myotis {Myotis ciliolabrum) at five 
mines, Western Long-eared Myotis (M evotis) at 
one mine, and Big Brown Bat (Eptesicusfuscus) 
at one mine. 

Summer ambient mine temperature was generally 
too cold (usually < 1 °C) to be suitable for 
maternity roosts. However, suitable sites were 
present in some underground workings, and one 
C. townsendii maternity roost averaged 1 1 .9 °C 
during June and July. Maximum mean daily 
temperature recorded in any mine was 1 4.6 °C. 

Ambient mine temperature decreased significantly 
as elevation increased, and summer and winter 
mine temperatures were highly con-elated and 
relatively predictable using time-series data. 



However, complex mines at higher elevations may 
contain internal microsites, not detectable from 
external surveys, with temperature and relative 
humidity regimes suitable at all seasons for roost- 
ing bats. 

Relative humidity fluctuated dramatically in many 
mines, and tended to be lowest and least stable in 
winter, when means in some mines were < 50%. 
At two known Townsend's Big-eared Bat hiber- 
nation roosts, winter mean relative humidity was 
74.0% and 83 .4%, while respective ambient mine 
temperatures averaged 7.5 °C and 4.4 °C. 

Mine suitability for roosting bats was not apparent 
from external variables, such as portal size, 
number of portals, detectable airflow, or even 
elevation. The most useful information obtained 
during external visual inspections was the presence 
or absence of obstructions at portals and the 
extent of underground workings, if visible from the 
portal. 

All mines should first be evaluated for use by bats 
before reclamation takes place. Useful informa- 
tion about the potential for roost use can be 
gathered from external inspections and monitoring 
(visual, auditory, trapping) at mine portals. How- 
ever, where possible and safe, the best method for 
assessing mine structure and use by bats is under- 
ground survey. Identifying mines suitable for 
hibernating bats requires underground inspection. 
Trapping at mine portals for pregnant and lactating 
females may be effective in identifying mines used 
as maternity roosts, but even here internal inven- 
tory is the best survey method. Mines that are 
used for night and day roosts can be effectively 
monitored on multiple visits without mine entry, 
preferably during different seasons, but even a 
single underground visit can reveal if there is any 
evidence of more extensive use by bats. 



Acknowledgements 



This project was funded through a Challenge 
Cost-Share agreement between the Bureau of 
Land Management Dillon Field Office and the 
Montana Natural Heritage Program, Montana 
State Library. Additional support was provided 
by the Montana Department of Environmental 
Quality Mine Waste Cleanup Bureau and the 
USGS-Biological Resources Division, 
Midcontinent Ecological Science Center. 

We were aided in the field by Sam Martinez, Tom 
O'Shea, Michelle Brown, and Janelle Corn. Tom 



O'Shea (USGS-BRD) kindly provided on loan 
some of the data loggers used during this study. 
We also thank Lee Flath (Lewis and Clark Cav- 
erns State Park) for granting access to the Gyp- 
sum adits, and Marian and Max Johnson (Ravalli) 
for permission to visit the McDonald Mine adits. 
Cedron Jones (MTNHP) produced the map. 

The report was reviewed and edited by John 
Carlson (MTNHP) and Joy Lewis (MTNHP), 
and produced with the help of Katrina 
Scheuerman(NRIS). 



11 



Table of Contents 



INTRODUCTION 1 

METHODS 1 

RESULTS ....2 

Mine habitat features 2 

Mine temperature and relative humidity. 2 

Bat use of mines 8 

DISCUSSION AND RECOMMENDATIONS 9 

Roost environments 9 

Management implications 11 

LITERATURE CITED 12 

APPENDIX 1 . Continuous temperature and relative humidity profiles for nine mines 15 

FIGURES AND TABLES 

Figure 1 . Map of mine sites 3 

Figure 2. Mean temperature decreases with increased elevation in winter 6 

Figure 3. Winter/summer ambient mine temperature 7 

Table 1 . Summary of physical and climatological characteristics of abandoned mines 4 

Table 2. Daily mine temperature and relative humidity- winter/summer. 5 

Table 3. Bats observed at abandoned mines 8 

Table 4. Summary of microclimate data for Townsend's Big-eared Bat (C. townsendii) 10 



ill 



INTRODUCTION 

Because bats spend much of their lives in roosts 
(Kunz 1 982), knowledge of their roosting require- 
ments provides important life-history information 
for understanding habitat use and seasonal pres- 
ence of most species. Furthermore, suitable 
summer and winter roosts may limit local and 
regional distribution and relative abundance of 
many temperate-zone bats (Humphrey 1 975, 
Dobkin et al. 1 995), especially cave-dwelling 
taxa. Thus conservation and protection of roosts 
are critical long-term management activities for the 
perpetuation of many North American bat species 
(Sheffield etal. 1992). 

Bat populations in many natural caves have 
declined or disappeared because of a variety of 
human-induced disturbances (LaVal and LaVal 
1 980, Richter et al. 1 993, Turtle and Taylor 
1 994). Abandoned and undisturbed mines now 
serve as principle summer and winter roosts for 
many cave-dwelling species (Turtle and Taylor 
1 994) because mines offer a variety of subterra- 
nean microclimates similar to those present in 
natural caves (Turtle and Stevenson 1 978). 
Concern about the status of North American bat 
populations increased dramatically in recent 
decades (Pierson 1 998) when it was recognized 
that significant numbers of abandoned mines were 
being barricaded, backfilled, and blasted shut for 
safety and liability reasons, without prior biological 
survey to determine their significance for roosting 
bats. 

We conducted a survey of abandoned mines on 
BLM lands in southwestern Montana during the 
summers of 1 997 and 1 998 (Hendricks et al. 
1 999) to assess and characterize their use by bats 
prior to potential reclamation activity. We antici- 
pated that our work would help managers identify 
sites currently used by bats, and that the informa- 
tion characterizing used abandoned mines might 
guide future mine survey and reclamation activity. 
We gathered long-term climate data from used 
abandoned mines because roost climate is a major 
influence on roost site use. Roost environment 



descriptions (especially temperature and relative 
humidity at roost microsites) are very limited for 
bats in Montana, and most available data pertain 
to roosts in caves (Worthington 1 99 1 , Madson 
and Hanson 1992, Hendricks 2000, Hendricks et 
al. 2000). 

For each mine inspected internally in 1 998 and 
considered safe for reentry we placed electronic 
data loggers to record daily mine temperature and 
relative humidity over a 6- 1 2 month period. Our 
objectives for this phase of the study were to: 1 ) 
document daily mine ambient temperature and 
relative humidity during winter and summer, 
especially at underground microsites where we 
found evidence of bat use, 2) determine the 
seasons when mines were used for roosting, and 
identify the bat species using the mines, and 3) 
determine mine characteristics documented from 
external surveys that might be useful for identifying 
underground environments that are suitable for bat 
roosts in abandoned mines. Of special interest 
were mines used by Townsend's Big-eared Bat 
(Corynorhinus townsendii) because this bat is a 
Montana animal species of special concern, a 
Montana BLM Special Status species, and a 
species of high conservation concern throughout 
its range (Pierson et al. 1 99 1 , Pierson et al. 1 999, 
Sherwin etal. 2000). 



METHODS 

We concentrated our study on ten mines between 
45°10 , Nand47°16 , N latitudes in southwestern 
Montana (Figure 1), six mines in Beaverhead, 
Madison, and Silver Bow counties, supplemented 
with four mines in Jefferson and Lake counties 
known or suspected to be used by Townsend's 
Big-eared Bat. Elevation of mines ranged from 
853 m to 2249 m (Table 1). Mines used by bats 
were identified first from historical records or by 
external inspection during summer, and through 
use of electronic bat detectors (ANAB AT II, 
Titley Electronics, Ballina, Australia) and mist-net 
or harp trap sampling at portals. 



We surveyed each mine internally at least twice to 
the fullest extent possible where deemed safe. No 
vertical workings (shafts) were entered during this 
study. At least two people entered each mine 
during surveys. We recorded presence, number, 
location, and identity of bat species when possible. 
During surveys, we recorded the following "struc- 
tural" habitat variables: vegetation cover at the 
mine, portal elevation, number and size of portals, 
length of underground workings, presence of 
standing water, cross-section dimensions of main 
tunnels, and number of levels. We ranked mine 
complexity as simple (main passage with non- 
branching side tunnels), moderate (main passage 
with branching side tunnels or < 3 levels), or 
complex (main passage with multiple branching 
side tunnels or > 2 levels). 

We gathered time-series temperature and relative 
humidity data by installing at least one data logger 
(HOBO H8, Onset Computer Corporation, 
Pocasset, Massachusetts) in each mine, usually 
near microsites where bats or bat sign were 
observed. In two shallow mines data loggers 
were placed where we considered the mine 
environment likely to be the most stable. Fifteen 
data loggers were placed in the mines; only two 
mines contained more than one data logger. Data 
loggers were attached to an extendable aluminum 
rod and positioned < 30 cm below the tunnel 
ceiling. Data loggers were set to record tempera- 
ture and relative humidity every six hours. We 
calculated daily means from these data and used 
daily mean values in the analyses we present in this 
report. 

Because of the small sample of mines studied our 
analyses are largely inferential. Where statistical 
analyses were performed we followed standard 
procedures (Sokal and Rohlf 1981) using Statistix 
version 2.0 (Analytical Software, Tallahassee, 
Florida). 



RESULTS 

Mine habitat features. Use by bats of aban- 
doned mines in our sample did not appear related 



in any obvious way to vegetation cover, mine size 
or complexity (Table 1 ), size or number of portals, 
or availability of standing water. All mines were in 
sagebrush or sagebrush intermixed with scattered 
conifers, and all mines had either one or two 
functional portals with dimensions that ranged from 
1 .2-2. 1 m high by 1 .2-2.0 m wide. Five of the 
mines contained standing water. Six mines 
(McDonald Adits #1 and #2, Gypsum Adits #1 
and #2, Union, Hendricks) had some form of gate 
at their portals. 

Mine temperature and relative humidity. We 

placed data loggers in six mines in September and 
retrieved them the following August (Table 1). At 
four mines we placed data loggers in December or 
January and retrieved them the following July. 
Data loggers failed to record for the duration of 
installation at two mines; in the GypsumAdit#l 
the logger failed to record any data, and in the 
Unnamed Adit #3 the logger became wet and 
ceased operation by March, 1 74 days after 
installation. Continuous temperature and relative 
humidity profiles are shown in Appendix 1 for all 
loggers that recorded any data. 

Maximum daily temperature recorded among the 
mines (Table 1) was 14.6 °C in late July at the 
Unnamed Adit #2. However, portions of some 
mines never achieved temperatures > 6 °C, even 
in summer (Appendix 1 ). The lowest mine tem- 
perature, -1 5.9 °C, was recorded in late Decem- 
ber; in general mine temperatures dropped below 
freezing only in mines or portions of mines where 
there was significant movement of air. In several 
mines, relative humidity reached lowest values 
near or below 30% during December or January 
while maximum values (85-1 00%) were recorded 
in July or September (Appendix 1 ). 

Table 2 shows mean temperature and relative 
humidity data from each mine for the same winter 
and summer time periods, thereby making com- 
parisons among mines the most meaningful. Mean 
temperatures for January through April varied from 
-1 .4 °C to 1 1 .8 °C, depending on the mine and 
location within the mine. Interestingly, the ex- 
tremes were found in the same mine, the 




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Figure 1 . Location of abandoned mines in southwestern Montana where 
mine climates were studied during 1 998-1 999. 



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Hendricks. Hie June to mid-July extremes in 
mean temperature (3.6 °C and 12.2 °C) also 
occurred in the Hendricks Mine. Extreme values 
occurred in this mine because of significant air 
movement through parts of the workings, while 
other parts experienced very little air movement. 
For all data logger locations, summer mean 
temperatures were 2.5 ± 2. 1 °C warmer than in 
winter. The same pattern was evident for relative 
humidity; summer means were 1 2. 1 ± 9.2% 
greater than in winter. However, in the Main Drift 
of the Hendricks Mine summer relative humidity 
was actually a few percent lower than in winter 
(Table 2), the only data logger location where this 
occurred. 

Mean mine temperature tended to decrease with 
increased elevation in both winter and summer 
(Figure 2), but relative humidity did not show a 
significant elevation trend for either period (winter: 
r = -0.364, P = 0.376; summer: r = -0.308, P = 
0.458). For both temperature and relative humid- 
ity, summer means were highly and positively 



correlated with winter means (Figure 3). How- 
ever, variation (measured as the standard devia- 
tion) in temperature and relative humidity for the 
winter and summer periods at each data logger 
location was only weakly correlated (r = 0.3 87, P 
= 0.191 and r = 0.165, P = 0.591). 

We noted significant airflow in three mines, the 
Union, Hendricks, and Unnamed Adit # 2, and 
slight airflow in the shallow location of the 
McDonaldAdit#l. In the Union and Hendricks 
mines, we never saw bats or concentrations of 
droppings where airflow was greatest (the first 
level of the Union, Graeter Tunnel and First Drift in 
the Hendricks), although scattered droppings were 
present in these portions of the mines (Table 2). 
Mean temperature difference between winter and 
summer was larger at locations where there was 
significant air movement (4.88 ± 1 .26 °C versus 
1.03 ± 0.70 °C: f = 7.19, df = 11, P < 0.001). 
Air movement did not have a similar effect on the 
mean difference in winter and summer relative 
humidity (t = 0.79, P = 0.444). 



Table 2. Daily mine temperature (°C) and relative humidity (%) for winter (10 Jan-30 
Apr) and summer (1 Jun-13 Jul). Values are means ± 1 standard deviation. Asterisk 
indicates location is a known bat hibernation site (winter) or a maternity/day roost site 
(summer). 



Mine 


Winter (n 


= 111 days) 


Summer (n 


= 43 days) 




Temp 


Ivfcl 


Temp 


RH 


McDonald Adit #1 (shallow) 


7.5 ±0.9* 


74.0 ± 9.4 


10.5 ± 0.4* 


97.4 ±2.7 


(deep) 


10.0 ±0.4 


98.2 ±1.4 


11.3 ±0.2* 


100.0 ±0.4 


McDonald Adit #2 


10.7 ±0.2 


89.0 ±2.0 


11.9±0.5* 


91.7 ±4.7 


Gypsum Adit #2 


4.4 ±0.9* 


83.4 ±4.2 


6.7 ±0.2 


97.8 ± 0.6 


Gypsum Adit #1 


— 









Unnamed Adit #2 


2.8 ± 1.7 


56.1 ±6.9 


9.2 ±1.5 


63.0 ± 13.0 


Unnamed Adit #3 


— 


_-_ 






Unnamed Adit #1 


7.2 ±0.4 


49.9 ±3.4 


8.7 ±0.5 


69.2 ±12.6 


Union 


2.8 ± 1.1 


59.2 ±7.6 


7.9 ±1.5 


74.4 ±14.7 


Hendricks First Drift 


-0.9 ±1.4 


71.7±9.6 


3.6 ±0.3 


84.5 ±2.1 


Graeter Tunnel 


-1.4 ±2.7 


69.8 ±9.9 


3.9 ±0.3 


86.2 ±1.7 


Main Drift 


9.1 ±0.2* 


77.5 ±2.0 


9.7 ±0.2 


74.7 ± 0.4 


Solution Cavity 


11.8±0.1 


42.6 ± 6.2 


12.2 ±0.0* 


65.2 ±2.0 


West Drift 


10.6 ±0.0 


44.0 ±6.8 


10.7±0.1* 


67.3 ±1.9 


Ruth & Copper Bottom 


4.1 ±0.4 

— i 


98.7 ±2.0 

, I 


4.9 ±0.2 


100.0 ±0.0 



Q. 
< 

C 
(0 

—) 

Q 

<u 

3 

(0 
w 


Q. 

E 
m 

<x> 

c 




600 800 1000 1200 1400 1600 1800 2000 2200 2400 

Mine elevation (m) 



c 

3 



O 

g) 

3 

S 

Q. 

E 
m 

c 




600 800 1000 1200 1400 1600 1800 

Mine elevation (m) 



2000 2200 2400 



Figure 2. Mean mine temperature decreases with increased elevation in winter (Jan- Apr: r - 
-0.744, P = 0.034) and summer (Jun-Jul: r = -0.828, P = 0.01 1) in southwestern Montana. Points are 
mean values for individual mines, using data from Table 2. Dashed line is the 95% confidence interval. 



3 

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Mine temperature (C): Jan-Apr 



12 



14 



100 



c 

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x: 
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= 60 - 




60 70 80 90 

Mine relative humidity (%): Jan-Apr 



100 



Figure 3. Winter (Jan-Apr) and summer (Jun-Jul) mine ambient temperature (top: Y= 0.608X + 4.874, R 2 
= 0.823) and relative humidity (bottom: Y = 0.657X + 36.201 , R 2 = 0.792) are highly correlated (P < 
0.00 1 ) in southwestern Montana. Points represent individual datalogger locations, using the data from Table 
2. Dashed line is the 95% confidence interval. 



7 



Bat use of mines. We observed four species of 
bats at the ten mines (Table 3). Corynorhinus 
townsendii was present at six mines, Myotis 
ciliolabrum at five mines, and M. evotis and 
Eptesicusfuscus at one mine each. In all cases, 
we observed only small numbers of individuals. 

Three of the mines (McDonald Adit #1 , Gypsum 
Adits #1 and #2) were hibernacula for C. 
townsendii, with number of hibernating individuals 
ranging from 1-8. A11C. townsendii in the 
McDonald Adit #1 were roosting singly on the 
walls < 1 .0 m above the floor within 40 m of the 
portal. In the Gypsum Adit #1 a single C. 
townsendii was on the wall <1 .0 m above the 
floor and 13.8m from the portal. In the Gypsum 
Adit #2 we found torpid bats (1 unidentified 
Myotis and 7 C. townsendii) between 6.0-25.5 
m from the portal; all bats were <1 .0 m above the 
floor and roosting singly. In the only other mine 
entered during winter (Hendricks) we found single 
M. ciliolabrum and E. fuscus, both about 1.5 m 
above the floor 143 m from the portal. A mater- 
nity roost of 25 C. townsendii in the McDonald 
Adit #2 was the largest number of bats we found 



in a single mine; these were in a tight cluster on the 
wall near the ceiling about 1.5 m above the floor 
and 14 m from the portal. We found no other 
maternity roosts. 

The remaining bats we observed or captured 
(Table 3) appeared to be using the mines as day 
or night roosts. The single M. ciliolabrum we 
found in June in the Hendricks Mine was a female 
fully exposed on the wall near the ceiling about 1 .5 
m above the ground. Three of five M. 
ciliolabrum we captured at the portal of the 
Unnamed Adit #1 on 11 June were non-lactating 
females (teats visible, however). The two M. 
evotis we captured in August at the Unnamed Adit 
#2 were lactating females, the only reproductive 
female bats we captured. All the other individuals 
that we handled were males. 

We were unable to fully survey the three largest 
mines, McDonald Adit # 1 , Hendricks Mine, 
Union Mine, although we investigated 60-70% of 
the workings in each. Therefore, it is possible, 
even probable, that we missed seeing some bats 
during summer in the McDonald Adit # 1 , and in 



Table 3. Bats observed during 1998-1999 at abandoned mines in southwestern Montana. 
An asterisk following a mine name indicates bats were captured at the mine portal. 



Mine 


Bat species 3 


McDonald Adit #1 (shallow) 


8 Corynorhinus townsendii (7 Dec), 1 Myotis species (13 Jul) 


(deep) 


1 C. townsendii (13 Jul) 


McDonald Adit #2 


25 C. townsendii (13 Jul) 


Gypsum Adit #2 


7 C. townsendii (6 Jan), 1 Myotis species (6 Jan) 


Gypsum Adit #1 


1 C. townsendii (6 Jan) 


Unnamed Adit #2* 


5 M. ciliolabrum (6 Aug, 17 Aug), 1 M. evotis (6 Aug, 17 Aug) 


Unnamed Adit #3* 


2 M. ciliolabrum (7 Aug) 


Unnamed Adit #1 * 


1 C. townsendii (11 Jun), 8 M. ciliolabrum (11 Jun) 


Union* 


1 C. townsendii (11 Jul), 2 M. ciliolabrum (1 1 Jul) 


Hendricks First Drift 


None (scattered droppings) 


Graeter Tunnel 


None (scattered droppings) 


Main Drift 


1 M. ciliolabrum (4 Dec), 1 Eptesicus fuscus (4 Dec) 


Solution Cavity 


None (concentrated droppings) 


West Drift 


1 M. ciliolabrum (13 Jun) 


Ruth & Copper Bottom 


None (few droppings) 



Townsend's Big-eared Bat Corynorhinus townsendii. Western Small-footed Myotis 
Myotis ciliolabrum, Western Long-eared Myotis Myotis evotis. Big Brown Bat Eptesicus 
fuscus. 



the Hendricks Mine during summer and especially 
in winter. Low netting success at the portal of the 
Union Mine, coupled with our internal survey, 
suggests to us that this mine is unlikely to support 
relatively large numbers of bats even in areas we 
did not reach. 

Bats were present during winter at locations with 
mean winter temperatures of 4.4-9. 1 °C and mean 
relative humidity between 74-84% (Table 2). 
Mine sites where we observed bats during the day 
in summer (either maternity or day roosts) were 
the warmest (1 0.5- 12.2 °C) among the data 
logger locations (t = 4.89, P < 0.00 1 ; adjusted for 
unequal variances). However, occupied sites in 
summer were not necessarily the most humid. 
Microclimate conditions at C. townsendii roosts 
(Tables 2 and 3, Appendix 1) were cold during 
winter (averages of 4.4 and 7.5 °C), but relatively 
warm during summer (1 1 .3 and 1 1 .9 °C). Rela- 
tive humidity at C. townsendii roosts averaged 
74.0 and 83 .4% in winter, 9 1 .7 and 1 00% in 
summer. 



DISCUSSION AND RECOMMENDA- 
TIONS 

Roost environments: Abandoned mines provide 
suitable environments for a variety of roosting 
purposes for bats (Pierson et al. 1 99 1 , Tuttle and 
Taylor 1 994, Berts 1 997, Sherwin et al. 2000). 
Abandoned mines in northwestern North America 
are often used as hibernacula and day or night 
roosts rather than maternity roosts because mine 
temperatures are too cold and energy-expensive 
for norma! rates of development of young bats 
(Dwyer 1971). The results of our study in south- 
western Montana of mine features and microcli- 
mates favored by bats, particularly C. townsendii, 
conform to general patterns for western North 
America. Our study was hampered by lack of 
visits to each mine during the four seasons to 
determine with certainty the seasonal use of each 
by bats. Nevertheless, we documented the long- 
term climate of several abandoned mines over an 



elevation gradient, and several preliminary conclu- 
sions regarding roost use by bats in this portion of 
Montana are possible. 

We found only one mine (McDonald Adit #2) 
used as a maternity roost, by C. townsendii, and 
it was at the lowest elevation of the mines studied 
(Table 1). Mean June- July temperature near this 
colony was about 12 °C (Table 2), which is much 
colder than at maternity sites in California (Pierson 
etal. 1991). It is possible the McDonald Adit #2 
maternity roost moved after our July visit to 
warmer temperatures nearer the mine portal. 
Similar behavior has been documented for Califor- 
nia maternity aggregations after young are bom in 
late July and early August (Pierson et al. 1 99 1 ). 
We did not get close enough to the McDonald 
colony to determine if young bats were present 
when we retrieved our data logger on 1 3 July. 
There are few temperature and relative humidity 
data for other C. townsendii maternity roosts in 
Montana. Temperature was 1 8 °C beneath a 
maternity roost of about 75 C. townsendii in a 
ceiling dome of Toeckes Cave (1 524 m elevation) 
on 23 August 1 999 (S. Martinez personal commu- 
nication). Temperature was likely at least a few 
degrees warmer closer to the roost. 

Summer bat use of mines declined with increased 
elevation in southwestern Montana (Hendricks et 
al. 1999). The most plausible explanation for this 
pattern is that mean mine temperature declined 
significantly as elevation increased (Figure 2), 
making higher elevation mines less attractive to 
bats for roosting. This is especially true for female 
bats (Cryan et al. 2000) because of increased 
energy demands related to reproduction. Bats 
found at high elevations in western North America 
tend to be males or non-reproductive females 
(Storz and Williams 1 996, Cryan et al. 2000). 
Currently, little is known about the upper elevation 
limit for caves and mines used by bats in Montana. 
Little Ice Cave (2493 m elevation) is the highest 
known hibernation roost in the state (Madson and 
Hanson 1 992). There is also considerable activity 
by several species of Myotis at the mouth of this 



cave in summer, although cave temperature 
throughout is 3 .3 °C (Worthington 1 99 1 ) making it 
too cold for use as a maternity roost. 

As our data across a range of elevations show 
(Table 2, Appendix 1 ), mines in western Montana 
generally provide relatively cold roost environ- 
ments for bats regardless of season. Greatest use 
of abandoned mines by bats in western Montana 
is for day/night roosts and hibernacula. Many 
abandoned mines in southwestern Montana 
present bats with a variety of summer microcli- 
mates (Table 2) and are used briefly as night 
roosts (Hendricks et al. 1 999), where meals are 
digested in relative safety. However, hibernacula 
are the best-documented roost climates in Mon- 
tana, although data are usually point (single date) 
samples, and bat species found hibernating often 
are unidentified to species. Fortunately, the 
exception is C. townsendii, because it is relatively 
easy to identify, even when torpid and undis- 
turbed. 

In Montana, C. townsendii use caves and mines 
across a broad range of elevations for hibernation 
roosts (Table 4). Torpid C. townsendii have 



been found from November through April in sites 
where the respective ranges of temperature and 
relative humidity are-1 .0-8.0 °C and 50-100% 
(see also Table 2). Number of hibernating indi- 
viduals at each of these sites (Table 4) was < 20, 
although larger winter numbers have been re- 
ported in appropriate winter roosts in the lower- 
elevation plains of eastern Montana (Swenson 
1 970), where few surveys have been conducted. 
The data presented in Table 4 suggest that roosts 
below 2000 m elevation may routinely support 
larger winter aggregations of C. townsendii. This 
pattern could arise because arid landscapes often 
favored by this species (Sherwin et al. 2000) are 
found at lower elevations in the region, or because 
maternity roosts are often < 20 km from hiber- 
nacula (Humphrey and Kunz 1 976, Kunz and 
Martin 1982, Dobkin et al. 1995) and are prob- 
ably more abundant at lower elevations. Microcli- 
mates for Montana hibernacula of C townsendii 
are similar to those reported in the literature from a 
number of western and midwestern states 
(Pearson et al. 1 952, Twente 1 955, Twente 1 960, 
Humphrey and Kunz 1976, Genter 1986, Pierson 
et al. 1991, Webb et al. 1 996, Choate and 
Anderson 1 997, Kuenzi et al. 1 999), with winter 



Table 4. Summary of point-sample (single date) microclimate data for Townsend's Big- 
eared Bat {Corynorhinus townsendii) hibernacula in Montana. Temperature (T) and 
relative humidity (RH) data were recorded near hibernating bats using a sling 
psychrometer. 



Locality 


Elev (m) 


Date 


No. bats 


T(°C) 


RH (%) 


Source" 


McDonald Adit #1 


853 


7 Dec 


8 


8.0 


57-64 


1 


Azure Cave 


1361 


12 Nov 


6 


6.0-7.0 


90-100 


2 


Gypsum Adit #2 


1390 


6 Jan 


7 


3.5-4.5 


80 


1 


Gypsum Adit #1 


1432 


6 Jan 


1 


6.0 


54 


1 


Tate-Poetter Cave 


1487 


19 Apr 


4 


2.0-3.0 


76-86 


3 


Toeckes Cave 


1524 


12 Feb 


9 


-1.0-3.0 


50-85 


4 


Four-eared Bat Cave 


1536 


26 Feb 


15 


6.5-7.0 


61-73 


5 


Frogg's Fault Cave 


1835 


28 Feb 


10 


6.5-7.0 


90 


5 


Dandy Mine 


1856 


4 Mar 


4 


5.0 


100 


5 


Lisbon Mine 


2012 


4 Mar 


1 


6.5 


100 


5 


Big Ice Cave 


2295 


18 Mar 


2 


-0.5 


100 


5 


Mystery Cave 


2384 


20 Mar 


3 


3.5 


85 


5 


a nthkstlldv 1QQR-1QOC 


): 2^ Hendric 


;ks et al. 20C 


0: 3) Hendr 


icks 2000; 4 


) unpublishec 





data, 2000; 5) Madson and Hanson 1992. 



10 



roost temperature typically ranging between -1 .5- 
10.0 °C. However, in some California locations 
roost temperature near torpid individuals may 
reach 2 1 .0-25.0 °C (Pierson et al. 1991, Webb et 
al. 1 996), much warmer than for any Montana 
hibernaculum. 

Management Implications: There are two 
major approaches for assessing abandoned mines 
for bats: external and internal surveys (Altenbach 
1 995, Navo 1 995). During external surveys data 
are gathered on the number and dimension of all 
entrances (portals), airflow, outside air tempera- 
ture, presence of standing water, and visual sign of 
bats (carcasses, roosting bats, droppings); one 
portal survey in spring, one in summer, and two in 
fall are recommended (Navo 1 995). Use of 
electronic bat detectors can aid in portal surveys. 
Internal surveys allow direct measurement of mine 
temperature and relative humidity, and also an 
assessment of the extent of underground workings 
and their configuration as well as evidence of bats 
at specific locations within the mine. Cold season 
internal surveys can determine both summer and 
winter use, whereas warm season surveys can 
determine only summer use. 

Our analysis identified few mine characteristics 
measurable from external surveys that are good 
predictors of mine suitability for bats, with the 
exception of obstructions across portals that inhibit 
or preclude bat access (Hendricks et al. 1 999). 
Mine temperature is an important feature for roost 
selection by bats (Dwyer 1 97 1 , Humphrey 1975), 
and relative humidity may also be important (Betts 
1 997). We found a significant negative relation- 
ship between elevation and summer or winter mine 
temperature (Figure 2), but not between elevation 
and relative humidity; mines at higher elevation 
were colder year round, but not necessarily less 
humid. Mean mine temperature during both 
summer and winter was highly correlated (Figure 
3), indicating that temperature taken during one 
season is a good predictor of temperature during 
the other season in the same mine; this pattern was 
also found for relative humidity. Nevertheless, 
obtaining these measurements required going 



underground. Furthermore, we found consider- 
able short-term variation in temperature and/or 
relative humidity in most of the mines we moni- 
tored (Appendix 1), making questionable the 
characterization of their year-round climate from 
data obtained during a single visit (Sherwin et al. 
2000). If surveys are restricted to one or two 
visits because of monetary or logistical limitations, 
the potential for significant short-term variation 
should be kept in mind when characterizing the 
mine climates. 

We also found that mines with climates largely 
unsuitable for use by bats may contain areas within 
them that can be and are used (Table 2, Appendix 
1 ). It is not possible to identify these internal 
microsites from external surveys, with the possible 
exception of the shallowest mines with workings 
completely visible from the portal. Identification of 
hibernacula, the most likely mine roosts to be used 
over several continuous months in Montana, is 
impossible from external survey alone. Further- 
more, internal survey is the quickest and least 
labor/time intensive method for determining mine 
suitability for bats in all seasons (Pierson et al 
1 999). We therefor suggest that, where safe, 
internal survey is the preferred method for assess- 
ing mine use and suitability for bats. Where mine 
entry is impossible or unsafe, external survey at the 
portal must suffice. In these cases it is critical that 
surveys are conducted at the appropriate time. 
Possible hibernation activity is detected best in fall 
(September and October) when bats swarm at 
their hibernation roosts. Maternity use of mines is 
detected best in summer (July and August) when 
females are pregnant or lactating. 

We recommend that all abandoned mines sched- 
uled for reclamation on public lands receive 
proper evaluation as bat habitat prior to closure, 
whether by external or internal survey. Protocols 
for mine evaluation are presented in the conserva- 
tion assessment and strategy for the Townsend's 
Big-eared Bat, C. townsendii (Pierson et al. 
1 999), as well as Altenbach (1 995) and Navo 
(1 995), and are appropriate for all mine-dwelling 
bat species in Montana. 



11 



LITERATURE CITED 

Altenbach, J. S. 1995. Entering mines to survey 
bats effectively and safely. Pp. 57-61 In 
Inactive mines as bat habitat: guidelines for 
research, survey, monitoring and mine 
management in Nevada (B. R. Riddle, 
ed.). Biological Resources Research 
Center, University of Nevada, Reno, NV. 

Betts, B. J. 1997. Microclimate in Hell's Canyon 
mines used by maternity colonies of 
Myotis yumanensis. Journal of Mammal- 
ogy 78:1240-1250. 

Choate, J. R., and J. M. Anderson 1 997. Bats of 
Jewel Cave National Monument, South 
Dakota. Prairie Naturalist 29:39-47. 

Cryan, P. M., M. A. Bogan, and J. S. Altenbach. 
2000. Effect of elevation on distribution 
of female bats in the Black Hills, South 
Dakota. Journal of Mammalogy 81:719- 

725. 

Dobkin, D. S., R. D. Gettinger, and M. G. 

Gerdes. 1995. Springtime movements, 
roost use, and foraging activity of 
Townsend's Big-eared Bat (Plecotus 
townsendii) in central Oregon. Great 
Basin Naturalist 55:315-321. 

Dwyer,P. D. 1971. Temperature regulation and 
cave-dwelling in bats: an evolutionary 
perspective. Mammalia 35:424-455. 



Hendricks, P., D. L. Genter, and S. Martinez. 

2000. Bats of Azure Cave and the Little 
Rocky Mountains, Montana. Canadian 
Field-Naturalist 114:89-97. 

Hendricks, P., D. Kampwerth, and M. Brown. 
1999. Assessment of abandoned mines 
for bat use on Bureau of Land Manage- 
ment lands in southwestern Montana: 
1997-1998. Unpublished report, Mon- 
tana Natural Heritage Program, Helena, 
MT. 29 p. 

Humphrey, S. R. 1975. Nursery roosts and 
community diversity of Nearctic bats. 
Journal of Mammalogy 56:321-346. 

Humphrey, S. R., and T. H. Kunz. 1976. Ecol- 
ogy of a Pleistocene relict, the Western 
Big-eared Bat {Plecotus townsendii), in 
the southern Great Plains. Journal of 
Mammalogy 57:470-494. 

Kuenzi, A. J., G. T. Downard, and M. L. 

Morrison. 1999. Bat distribution and 
hibernacula use in west central Nevada. 
Great Basin Naturalist 59:21 3-220. 

Kunz,T.H. 1982. Roosting ecology of bats. 

Pp. 1-55 In Ecology of Bats (T. H. Kunz, 
ed.). Plenum Publishing, New York, NY. 

Kunz,T.H., and R.A.Martin. 1982. Plecotus 
townsendii. Mammalian Species No. 
175:106. 



Genter, D. L. 1 986. Wintering bats of the Upper 
Snake River Plain: occurrence in lava-tube 
caves. Great Basin Naturalist 46:241- 

244. 

Hendricks, P. 2000. Preliminary bat inventory of 
caves and abandoned mines on BLM 
lands, Judith Mountains, Montana. Un- 
published report, Montana Natural 
Heritage Program. Helena, MT. 21 p. 



LaVal, R. R., and M. L. LaVal. 1980. Ecological 
studies and management of Missouri bats, 
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Missouri Department of Conservation 
Terrestrial Series #8. 

Madson, M., and G. Hanson. 1 992. Bat hiber- 
naculum search in the Pryor Mountains of 
south-central Montana, February and 
March 1992. Unpublished report, Mon- 
tana Natural Heritage Program. Helena, 
MT. 35 p. plus appendices. 



12 



Navo,K. 1995. Guidelines for external surveys 
of mines for bat roosts. Pp. 49-54 In 
Inactive mines as bat habitat: guidelines for 
research, survey, monitoring and mine 
management in Nevada (B. R. Riddle, 
ed.). Biological Resources Research 
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Pearson, O. P., M. R. Koford, and A. K. 

Pearson. 1952. Reproduction of the 
Lump-nosed Bat {Corynorhinus 
rafinesquei) in California. Journal of 
Mammalogy 33:273-320. 

Pierson, E. D. 1 998. Tall trees, deep holes, and 
scarred landscapes: conservation biology 
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Bat biology and conservation (T. H. Kunz 
andP.A.Racey,eds.). Smithsonian 
Institution Press, Washington, D.C. 

Pierson, E. D., W. E. Rainey, and D. M. Koontz. 
1 99 1 . Bats and mines: experimental 
mitigation for Townsend's Big-eared Bat 
at the McLaughlin Mine in California. Pp. 
3 1-42 In Proceedings V: Issues and 
technology in the management of impacted 
wildlife. Thome Ecological Institute, 
Aspen, CO. 

Pierson, E. D., M. C. Wackenhut, J. S. 

Altenbach, P. Bradley, P. Call, D. L. 
Genter, C. E. Harris, B. L. Keller, B. 
Lengus, L. Lewis, B. Luce, K. W. Navo, 
J. M. Perkins, S. Smith, and L. Welch. 
1 999. Species conservation assessment 
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and Corynorhinus townsendii 
pallescens). Idaho Conservation Effort, 
Idaho Department of Fish and Game, 
Boise, Idaho. 63 p. 



Richter, A. R., S. R. Humphrey, J. B. Cope, and 
V. Brack, Jr. 1993. Modified cave 
entrances: thermal effect on body mass 
and resulting decline of endangered 
Indiana Bats (Myotis sodalis). Conserva- 
tion Biology 7:407-41 5. 

Sheffield, S. R., J. H. Shaw, G A. Heidt, and L. 
R. McClenaghan. 1992. Guidelines for 
the protection of bat roosts. Journal of 
Mammalogy 73 :707-7 1 0. 

Sherwin, R. E., D. Stricklan, and D. S. Rogers. 
2000. Roostmg affinities of Townsend's 
Big-eared Bat {Corynorhinus 
townsendii) in northern Utah. Journal of 
Mammalogy 8 1 :939-947. 

Sokal,R.R.,andF.J.Rohlf. 1981. Biometry, 
second edition. W. H. Freeman. San 
Francisco, CA. 

Storz, J. F., and C. F. Williams. 1 996. Summer 
population structure of subalpine bats in 
Colorado. Southwestern Naturalist 

41:322-324. 

Swenson,J.E. 1970. Notes on distribution of 
Myotis leibii in eastern Montana. Blue 
Jay 28:173-174. 

Turtle, M. D., and D. E. Stevenson. 1978. 

Variation in the cave environment and its 
biological implications. Pp. 108-121 In 
1 977 National cave management sympo- 
sium proceedings (R. Zuber, J. Chester, S. 
Gilbert, and D. Rhodes, eds.). Adobe 
Press, Albuquerque, NM. 

Turtle, M. D., and D. A. R. Taylor. 1 994. Bats 
and mines. Bat Conservation Interna- 
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Twente, J. W, Jr. 1955. Some aspects of habitat 
selection and other behavior of cavern- 
dwelling bats. Ecology 36:706-732. 



13 



Twente,J.W. 1960. Environmental problems 
involving the hibernation of bats in Utah. 
Proceedings of the Utah Academy of 
Science 37:67-71. 

Webb, P. I., J. R. Speakman, and P. A. Racey. 
1996. Howhotisahibernaculum? A 
review of the temperatures at which bats 
hibernate. Canadian Journal of Zoology 
74:761-765. 

Worthington, D. J. 1991. Abundance, distribu- 
tion, and sexual segregation of bats in the 
Pryor Mountains of south central Mon- 
tana. Unpublished thesis, University of 
Montana. Missoula, MT. 41 p. 



14 



Appendix 1. Continuous temperature (solid line) 
and relative humidity (broken line) profiles for 
1 998- 1 999 from nine mines in southwestern 
Montana (see Table 1 for additional details). 
Note that scales vary from figure to figure and that 
time periods of continuous recordings also vary. 
Townsend's Big-eared Bat {Corynorhinus 
townsendii) was documented underground at the 
first four locations (McDonald Adit #2, McDonald 
Adit #1 both sites, Gypsum Adit #2) and captured 
in summer at the portals of the next two locations 
(Unnamed Adit #1, Union Mine). McDonaldAdit 
#2 was a maternity site. 



15 



McDonald Adit #2 



15 
14 
13 

12 - 

n 

? 10- 

<u 

a. 

E 9- 

v 






o 




E 
I 



Apr 
Date 



May 



McDonald Adit #1 (Shallow) 



14 - 

12 - 

10 • 
O 
0) 8 • 



E 




McDonald Adit #1 (Deep) 




E 

I 



16 



Gypsum Adit #2 



15 
14 
13 
12 
11 
10- 

9- 

8 

7 -] 

6 

M 

4 
3 

2 
' 1 - 

Jan 






n 



^ 




Feb Mar Apr May Jun Jul 

Date 



■ 100 

• 90 
-80 



-70 2 

E 

3 

I 

-60 



Unnamed Adit #1 




E 

3 
I 



Union 




Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul 
Date 



Aug Sep 



17 



Unnamed Adit #2 



E 




Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep 

Date 



Unnamed Adit #3 



15 

14 - 

13 

12 

11 

10 

9 - 

8- 

7 

6- 

5 

4 

3 

2 

1 - 






E 
I 



Dec 
Date 



Ruth & Copper Bottom 




Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep 
Date 



18 



Hendricks Graeter Tunnel 



Hendricks First Drift 




Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep 
Date 




Hendricks Main Adit 



Hendricks Solution Cavity 




Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep 
Date 









,-v 



r 



80 

- 70 
60 

- 50 
40 
30 



Oct Nov Dec Jan Feb Mar Apr May Jun Ju! Aug Sep 
Date 



Hendricks West Drift 



14 - 
13 - 
12 • 
11 




10 
9- 
8 ■ 

7 - 
6 • 
5 - 
4 - 
3 - 
2 - 
1 - 
- 


TT"^ u ■■ 

A 

Vtf . „ A" 

II ^ 

w 


..v*""~ 



100 
90 



Sep 



Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep 
Date 



19